Is ‘bad’ grammar a tell ?

I realized a while back that I base decisions about whether to trust an expert on the expert’s writing style.

Specifically: I instantly trust experts whose writing style signals that they want to be understood by non-specialists. I feel, intuitively, that they:

a) know what they’re talking about, and
b) want me to know, too.

I’m a bit more cautious when it comes to experts whose writing style signals that they don’t care one way or the other. 1

Experts who seem actively to wish readers not to have the first clue what they’re on about are another category altogether. Zero trust, plus a big round zero on the feeling thermometer.

Extended lean toolkit for total productivity,” for instance. No. Go away.

Having a reflexive trust in clear writing is the reason I came to own a copy of Siegfried Engelmann’s Teach Your Child to Read in 100 Easy Lessons years before I knew anything about phonics and/or the reading wars. His prose. Engelmann’s prose told me that he wanted everyone who picked up the book to understand every word in it. 

So I trusted he knew what he was talking about.

Recently, I’ve realized that I also use non-standard grammar as a tell. I take non-standard grammar, in speech and in text, as a sign of authenticity. 

By non-standard, I mean constructions like: “I am making this statement on behalf of me and my sister.”

Obviously, “me and my sister” is standard for the person using this construction. But it’s not Standard Written Englishand because it’s not, I reflexively assume the speaker (or writer, in the case I’m thinking about) is telling the truth as he sees it. 

Another example: “wrong” participles.

I heard a politician, a few weeks ago, use the construction “If we had went to that meeting.”

None of his colleagues say things like “if we had went,” and the fact that he does makes me see him as truthful in a way I don’t see the others as truthful. I see him as not “polished,” not “slick.”

I have no idea whether I should be making such judgments, of course (although I’m pretty sure the nothing-to-hide principle works in the case of education writers). 

But here’s my question: if a person wanted to fake authenticity by using non-standard grammar, could he or she do it ?

I’m pretty sure Katie can, but I’m pretty sure I can’t. 1

Which makes me think your average person can’t fake grammar. 

Your average person can lie.

Average people can lie about what they’re doing or thinking or planning or hiding.

But they can’t lie about what participles they use. 
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1. Katie’s a linguist.